The present invention generally relates to monitoring the condition of machine tools by acoustic emission detection and, more particularly, is concerned with improvements in the design of acoustic emission transducers and in the mounting thereof to the support structures of machine tools, such as used in metalcutting processes.
Materials under stress, experiencing fracture and cracking, are known to produce wave-like bursts of strain energy, commonly referred to as stress wave or acoustic emission. This phenomenon has been employed heretofore to monitor the operating conditions of machine tools, such as lathes, drilling machines, metalcutting tools and the like, to detect tool deterioration and damage, for instance, due to crack growth. Representative patents related to detection of acoustic emission for monitoring tool condition during operation are the devices, disclosed in U.S. Patents to Keledy et al, (U.S. Pat. No. 3,713,127), Feng (U.S. Pat. No. 4,011,472), Moore (U.S. Pat. No. 4,563,897) and Ohnuki et al (U.S. Pat. No. 4,574,633).
However, commercially-available acoustic emission transducers have mostly been developed for well-established acoustic emission monitoring applications, such as defect detection. These transducers are not designed ideally for detecting the acoustic emission signals encountered in machining, nor designed appropriately for installation in association with a machine tool. For instance, one presently-available transducer has a smooth-surfaced cylindrical configuration and is placed in a pocket machined out of the supporting structure, such as the shank, of the machine tool. A couplant is used with a compliant element to keep the transducer against the wall of the pocket. Although this particular transducer functions reasonably well in practice, it has several limitations which adversely impact its performance and versatility. The principal limitations include: first, the necessity of hand fitting the transducer during assembly to ensure uniform transducer mounting from machine tool to machine tool; second, the difficulty of putting strain relief on the cable of the transducer; and, third, the necessity to adopt several different installation methods depending on the machine tool being instrumented.
Consequently, a need exists for improvements in the design and mounting of acoustic emission transducers which will overcome these deficiencies and facilitate their application in the machine tool environment.